Planetary de-rotation system for a shaft fairing system

ABSTRACT

A de-rotation system includes a planetary gear set, and a fairing support structure mounted for rotation with a first ring gear.

BACKGROUND

The present invention is directed to a de-rotation system for a shaftfairing mounted between an upper hub fairing and a lower hub fairing.

The aerodynamic drag associated with a rotor hub of a rotary-wingaircraft is a significant portion of the overall aircraft drag,typically 25 percent to 30 percent for conventional single-rotorhelicopters. The rotor system drag increases for a rotary-wing aircrafthaving a counter-rotating, coaxial rotor system primarily due to thedual rotor hubs and the interconnecting main rotor shaft assembly. Forhigh-speed rotary wing aircraft, the increased drag resulting from thecounter-rotating, coaxial rotor system may result in a relativelysignificant power penalty.

The aerodynamic drag of the dual counter-rotating, coaxial rotor systemis generated by three main components—the upper rotor hub assembly, thelower rotor hub assembly, and the interconnecting main rotor shaftassembly. The drag contribution may be approximately 40 percent for eachof the hubs, and 20 percent for the interconnecting main rotor shaftassembly. Typically, a rotor hub fairing arrangement is mounted to eachof the upper rotor hub and the lower rotor hub such that overall drag onthe rotorcraft is reduced. The interconnecting main rotor shaft betweenthe upper rotor hub assembly and the lower rotor hub assembly, however,is typically exposed.

For a variety of reasons including, but not limited to, reduced drag andlow observability, a shaft fairing has been developed to streamline theexposed interconnecting main rotor shaft. The shaft fairing is mountedto the counter-rotating, coaxial rotor system within a rotationalenvironment between the upper hub fairing and the lower hub fairingthrough a bearing arrangement such that the shaft fairing is alignedwith the fuselage in forward flight but is free to align with therelative wind during low speed maneuvering.

During some flight conditions, the shaft fairing may undesirably rotaterelative the airframe. Rotation of the shaft fairing may increase dragand reduce the low-observability benefits of the shaft fairing.

SUMMARY

A de-rotation system for a fairing system according to an exemplaryaspect of the present invention includes a first ring gear defined aboutan axis, a second ring gear defined about the axis, a planetary gear setin meshing engagement with the first ring gear and the second ring gear,a cage assembly which supports the planetary gear set, and a fairingsupport structure mounted for rotation with the first ring gear.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1A is a general schematic view of an exemplary rotary wing aircraftembodiment for use with exemplary embodiments of the present invention;

FIG. 1B is a general perspective of a counter-rotating coaxial rotorsystem mounting a rotor hub fairing system;

FIG. 1C is an expanded partial phantom view of a counter-rotatingcoaxial rotor system mounting a rotor hub fairing system according to anexemplary embodiment of the present invention;

FIG. 2A is a perspective view of a counter-rotating coaxial rotor systemillustrating a de-rotation system;

FIG. 2B is an expanded perspective view of the de-rotation systemillustrated in FIG. 2A;

FIG. 3A is a top schematic view of a lower ring gear of an exemplaryde-rotation system;

FIG. 3B is a top schematic view of an upper ring gear of the de-rotationsystem of FIG. 3A; and

FIG. 4 is a perspective view of another exemplary de-rotation systemwith an active control.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1A illustrates an exemplary vertical takeoff and landing (VTOL)rotary-wing aircraft 10 having a dual, counter-rotating, coaxial rotorsystem 12 which rotates about an axis of rotation A. The aircraft 10includes an airframe 14 which supports the dual, counter rotating,coaxial rotor system 12 as well as an optional translational thrustsystem 30 which provides translational thrust generally parallel to anaircraft longitudinal axis L. Although a particular aircraftconfiguration is illustrated in this non-limiting embodiment, othercounter-rotating, coaxial rotor systems will also benefit from thepresent invention.

The dual, counter-rotating, coaxial rotor system 12 includes an upperrotor system 16 and a lower rotor system 18. Each rotor system 16, 18includes a plurality of rotor blades 20 mounted to a rotor hub 22, 24for rotation about a rotor axis of rotation A. A plurality of the mainrotor blades 20 project substantially radially outward from the hubassemblies 22, 24. Any number of blades 20 may be used with the rotorsystem 12.

A main gearbox 26 which may be located above the aircraft cabin 28drives the rotor system 12. The translational thrust system 30 may bedriven by the same main gearbox 26 which drives the rotor system 12. Themain gearbox 26 is driven by one or more engines (illustratedschematically at E). The gearbox 26 may be interposed between the gasturbine engines E, the rotor system 12 and the translational thrustsystem 30.

The translational thrust system 30 may be mounted to the rear of theairframe 14 with a rotational axis T oriented substantially horizontaland parallel to the aircraft longitudinal axis L to provide thrust forhigh-speed flight. The translational thrust system 30 includes a pusherpropeller 32 mounted within an aerodynamic cowling 34. Although a tailmounted translational thrust system 30 is disclosed in this illustratednon-limiting embodiment, it should be understood that any such system orother translational thrust systems including tractor and pod mountedsystems may alternatively or additionally be utilized.

The rotor system 12 includes a rotor hub fairing system 36 generallylocated between and around the upper and lower rotor systems 16, 18 suchthat the rotor hubs 22, 24 are at least partially contained therein. Therotor hub fairing system 36 provides significant drag reduction in whichlarge-scale flow separation is greatly reduced.

The rotor hub fairing system 36 generally includes an upper hub fairing38, a lower hub fairing 40 and a shaft fairing 42 therebetween (alsoillustrated in FIG. 1B). The rotor hub fairing system 36 is integratedsuch that the shaft fairing 42 generally follows the contours of theupper hub fairing 38 and the lower hub fairing 40 at the rotationalinterfaces therebetween to reduce interference effects between theseparate fairings 38, 40, 42 and minimize flow separation in thejunction areas. Furthermore, the lower hub fairing 40 is integrated withthe airframe 14 in an area typically referred to on a rotorcraft as apylon 14D (see FIG. 1C). It should be understood that fairing systems ofvarious configurations will be usable with the exemplary embodiments ofthe present invention presented herein.

Referring to FIG. 1C, the shaft fairing 42 may be mounted to thecounter-rotating, coaxial rotor system 12 through a bearing arrangement43U, 43L (illustrated schematically) such that the shaft fairing 42 maybe positioned at a relative angular position about the axis of rotationA relative the airframe 14 by a de-rotation system 44. The upper bearingarrangement 43U and the lower bearing arrangement 43L may berespectively located adjacent an upper portion and a lower portion ofthe shaft fairing 42. The upper bearing arrangement 43U may be attachedto one rotor shaft 12U while the lower bearing arrangement 43L attachedto the other rotor shaft 12L such that bearings in the arrangements 43U,43L are counter rotating and the net bearing drag is relatively low.

The de-rotation system 44 controls the position of the shaft fairing 42about the axis of rotation A such that the shaft fairing 42 remains in adesired azimuthal position relative the airframe 14. Although exemplaryembodiments of the present invention are described in connection with aparticular non-limiting aircraft embodiment, it should be readilyappreciated that other systems which require a stationary fairing in arotational environment will also benefit herefrom.

Referring to FIG. 2A, the de-rotation system 44 generally includes aplanetary gear system 46 to control a rotational position of the shaftfairing 42 (see e.g., FIG. 1C). The planetary gear system 46 generallyincludes a first ring gear 48, a second ring gear 50, a planetary gearset 52 a cage assembly 54 and a fairing support structure 56.

The second ring gear 50 is rotationally fixed to the airframe 14 thoughattachments 14A or such like. The first ring gear 48 is mounted to theinter-rotor fairing support structure 56 which is mounted to the shaftfairing 42.

The planetary gear system 46 generally includes a multitude of planetgear assemblies 58. Each planet gear assembly 58 includes an upperplanet gear 60, a lower planet gear 62 and an interconnect shaft 64 thatrotationally connects the upper planet gear 60 and the lower planet gear62. The upper planet gear 60 is in meshing engagement with the innerdiameter of the first ring gear 48 and the lower planet gear 62 is inmeshing engagement with the inner diameter of the second ring gear 50.Although four planet gear assemblies 58 are illustrated in thenon-limiting embodiment shown in FIGS. 2A and 2B, it should beunderstood that other numbers of assemblies may alternatively beprovided—typically one planet gear assembly 58 would be located betweeneach pair of main rotor blades.

The multitude of planet gear assemblies 58 are supported by the cageassembly 54. The cage assembly 54 includes an upper interface 54U andlower interface 54L (also illustrated in FIG. 2B) which support theplanetary gear set 52. The upper interface 54U and the lower interface54L are mounted to the main rotor system 12 for rotation therewith. Theupper interface 54U may be mounted to the lower bearing 43L or otherrotational support. That is, the upper interface 54U is axiallyretrieved and rotationally supported by the lower bearing 43L.

In operation, with reference to FIG. 3A, as the cage assembly 54 isrotated by the main rotor system 12, the lower planet gears 62 reactwith the fixed second ring gear 50 to rotate each planet gear assembly58 about each of their respective planet axes P. The upper planet gear60 of each planet gear assembly 58 is thereby rotated by theinterconnect shaft 64. The upper planet gear 60 rotates the first ringgear 48 in an equal but opposite direction of the cage assembly 54 (FIG.3B). Rotation of the first ring gear 48 rotates the inter-rotor fairingsupport structure 56 to rotate the shaft fairing 42 such that the shaftfairing 42 maintains a stable azimuthal position relative the airframe14. That is, the first ring gear 48 and the attached shaft fairing 43appear stationary to the fixed airframe 14

The de-rotation system 44 is a passive system that derives mechanicalinput from the main rotor system 12. The power required is minimal asfriction is the only opposing force and gear meshes are noted asefficient power transfer mechanisms. Since the fixed and rotating ringgears are rigidly connected via a gear and shaft arrangement, thede-rotation system 44 will maintain alignment, regardless of main rotorRPM variations.

Referring to FIG. 4, another de-rotation system 44′ provides an active,in-flight adjustable position capability. That is, the second ring gear50′ is azimuthally positionable relative the airframe 14. A drive system70 controls the rotational position of a second ring gear 50′ relativethe airframe 14 (FIG. 1C) in response to a control system 72. Thecontrol system 72 may be in communication with a shaft fairing positionsensor 74 and a flight control system 76 to azimuthally position thesecond ring gear 50′ and thus the shaft fairing 42 relative the airframe14 throughout all flight regimes to, for example, actively align theshaft fairing 42 with prevailing wind conditions during particularflight regimes.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to an illustrated attitude of the structure and shouldnot be considered otherwise limiting.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from theexemplary embodiments of the present invention.

The foregoing description is exemplary rather than defined by thesubject matter within. Many modifications and variations of the presentinvention are possible in light of the above teachings. Although certainembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

1. A de-rotation system comprising: a first ring gear defined about anaxis; a second ring gear defined about said axis; a planetary gear setin meshing engagement with said first ring gear and said second ringgear; a cage assembly which supports said planetary gear set; and asupport structure mounted for rotation with said first ring gear.
 2. Thesystem as recited in claim 1, wherein said second ring gear is fixedrelative to said axis.
 3. The system as recited in claim 1, wherein saidplanetary gear set is in meshing engagement with an inner diameter ofsaid first ring gear and an inner diameter of said second ring gear. 4.The system as recited in claim 1, wherein said planetary gear setcomprises a multitude of planet gear assemblies.
 5. The system asrecited in claim 4, wherein each of said multitude of planet gearassemblies comprise an upper planet gear, a lower planet gear and ashaft that rotationally connects said upper planet gear and said lowerplanet gear.
 6. The system as recited in claim 1, further comprising adrive system which selectively rotates said second ring gear.
 7. Thesystem as recited in claim 6, further comprising a control system incommunication with said drive system to selectively rotate said secondring gear to azimuthally position said second ring gear in response to aflight control system.
 8. A fairing system comprising: a shaft fairingmounted for rotation about an axis of rotation; and a planetary gear setconfigured to control a position of said shaft fairing about said axisof rotation.
 9. The system as recited in claim 8, further comprising: anupper hub fairing defined about said axis; and a lower hub fairingdefined about said axis, wherein said shaft fairing is mounted forrelative rotation between said upper hub fairing and said lower hubfairing.
 10. The system as recited in claim 8, wherein said planetarygear set further comprises: a first ring gear defined about said axis; asecond ring gear defined about said axis; a planetary gear set inmeshing engagement with said first ring gear and said second ring gear;a cage assembly which supports said planetary gear set; and a fairingsupport structure mounted for rotation with said first ring gear andsaid shaft fairing.
 11. The system as recited in claim 10, furthercomprising a drive system which selectively rotates said second ringgear.
 12. The system as recited in claim 11, further comprising acontrol system in communication with said drive system to selectivelyrotate said second ring gear to azimuthally position said second ringgear in response to a flight control system.
 13. The system as recitedin claim 10, wherein said second ring gear is fixed relative to saidaxis.
 14. A coaxial rotor system comprising: a lower rotor hub mountedto a lower rotor shaft which is configured to rotate about an axis ofrotation; an upper rotor hub mounted to an upper rotor shaft which isconfigured to rotate about said axis of rotation, said upper rotor shaftmounted through said lower rotor shaft and rotating in a directionopposite a direction of rotation of the lower rotor shaft; an upper hubfairing mounted at least partially about said upper rotor hub; a lowerhub fairing mounted at least partially about said lower rotor hub; ashaft fairing mounted between said upper hub fairing and said lower hubfairing for rotation about said axis of rotation; a planetary gear setconfigured to control a position of said shaft fairing about said axisof rotation.
 15. The system as recited in claim 14, wherein saidplanetary gear set further comprises: a first ring gear defined aboutsaid axis; a second ring gear defined about said axis; a planet gearassembly in meshing engagement with said first ring gear and said secondring gear; a cage assembly which supports said planet gear assembly; anda fairing support structure mounted for rotation with said first ringgear and said shaft fairing.
 16. The system as recited in claim 15,further comprising a drive system which selectively rotates said secondring gear.
 17. The system as recited in claim 16, further comprising acontrol system in communication with said drive system to selectivelyrotate said second ring gear to azimuthally position said second ringgear in response to a flight control system.
 18. The system as recitedin claim 15, wherein said second ring gear is fixed relative to saidaxis.
 19. The system as recited in claim 15, wherein said cage assemblyrotates with said lower rotor hub.
 20. An aircraft comprising: a lowerrotor hub mounted to a lower rotor shaft and configured to rotate aboutan axis of rotation; an upper rotor hub mounted to an upper rotor shaftand configured to rotate about said axis of rotation, said upper rotorshaft mounted through said lower rotor shaft and rotating in a directionopposite a direction of rotation of the lower rotor shaft an upper hubfairing mounted at least partially about said upper rotor hub; a lowerhub fairing mounted at least partially about said lower rotor hub; ashaft fairing mounted between said upper hub fairing and said lower hubfairing for rotation about said axis of rotation; a planetary gear setconfigured to control a position of said shaft fairing about said axisof rotation.
 21. The aircraft as recited in claim 20, wherein saidaircraft is a helicopter.